Effect of rock phosphate and plant growth-promoting rhizobacteria on physical and chemical properties change of corn residues during composting

Abstract

This study aims to study the effect of adding rock phosphate and plant growth-promoting rhizobacteria (PGPR), in the physical and chemical properties of the corn residues compost during aerobic decomposition. Four composting heaps were included in this study as it follows, 1) traditional method composting heap (T1), 2) heap was supplied with rock phosphate (T2), 3) heap was supplied with rock phosphate + Bacillus megatherum culture (T3), and 4) heap was supplied with rock phosphate+(Bacillus.megatherum, Azospirillum lipoferum, Azotobacter chroococcum) mixed cultures (T4). All compost treatments showed an increase in temperature right after composting started. The heap treated with three bacterial inoculums (T4) reached the highest peak values of 62.2°C on day 12 compared to other treatments. At the end of the composting period T1 recorded the lowest value of bulk density (533 kg/m3) compared to other treatments. The pH value declined to stabilize with the end result at 100 days being 6.9, 7.4, 7.1 and 7.0 for composting treatment T1, T2, T3 and T4, respectively. The initial C/N ratio was 61:1 for all composting treatments, and the final values of total C/N ratio after the 100 days were 15:1, 14:1, 12:1 and 10:1 for composting treatments T1, T2, T3 and T4 respectively. Compost supplied with rock phosphate and three bacterial inoculums (T4) reached has more N, P and K content compared to other composting treatments T1, T2, T3. These results indicated that adding rock phosphate and (PGPR) to corn residues during composting improve nutritional value of the resulting compost.